All cancers occur when cells multiply uncontrollably and anal and colon cancers are no different. However, they are not the same. They originate from different sections of the gut and have different symptoms, diagnostic methods, treatment options, and survival rates.
So in this post, let’s explore the key differences and similarities between anal and colorectal cancers.
What is colon cancer?
Colorectal cancer arises from cells that line the lumen of the large intestine. These cells are known as mucosal cells. The United States sees more than 150,000 new cases of colon cancer every year, making it the fourth most common cancer in the country.
What is anal cancer?
Anal cancer arises from cells of the anus. The anal canal is the last part of the intestine and is approximately 4 centimeters long. Cancer that arises within these 4 centimeters is referred to as anal cancer.
The good news is that anal cancer is much rarer than colon cancer. According to the American Cancer Society, there are 10,000 new anal cancer cases in the United States every year.
Anal cancer vs. colon cancer: who is at risk?
Factors that increase the risk of anal cancer do not necessarily also increase the risk of colon and rectal cancer. But some overlap might exist. Let’s take a look:
- Smoking: Smoking is a risk factor for both cancers. Cigarette smoke is full of carcinogens (another name for cancer-causing molecules) and is associated with many cancers in the body, including anal and colon and rectal cancers.
- Human papillomavirus (HPV) infection: HPV is the most important risk factor for anal cancer. The virus infects skin cells and can lead to anal cancer when it affects the anal skin. This is especially true for HPV types 16 and 18. However because the colon is not exposed to the outside, HPV is not associated with colon cancer.
- Weakened immune system: A weak immune system — such as in patients with AIDS — can also increase the risk of anal cancer.
- Obesity: This is a risk factor for colon cancer. Excess fat in the body increases fat-specific hormones, which can increase the risk of colon cancer.
- Inflammatory bowel disease (IBD): This is a risk factor for colon cancer. IBD causes repeated cycles of inflammation, which damages the colon. This can increase the risk of colon cancer, especially if someone has had the disease for more than 10 years.
- Family history: Having a first-degree relative with colon cancer can significantly increase the risk of colon cancer. Diseases like Familial Adenomatous Polyposis and Lynch Syndrome occur when certain genetic mutations run in a family. These mutations can increase the risk of multiple cancers, including colon cancer.
Anal cancer vs. colon cancer: what are the symptoms?
There are some “red flag” symptoms that are common to many cancers. At the same time, we have symptoms specific to each cancer type. Let’s look at and compare the symptoms of anal cancer and colon or rectal cancer.
- Weight loss: Weight loss is common to many cancers. Whether it is colon cancer or anal cancer, sudden weight loss over a period of months or weeks is a classic symptom to look out for.
- Fatigue: Fatigue is another non-specific symptom for many ailments, including both anal and colon cancers.
- Blood in the stool: The presence of blood in the stool is a symptom of colon cancer as well as anal cancer. However, the appearance of stool may be different in both types of cancer. In the case of colon cancer, blood is often mixed with the stool. This is unlike anal cancer, where blood usually “coats” the stool.
- Change in bowel habits: New diarrhea or constipation can point towards colon cancer. When colon cancer grows, it can obstruct the bowel causing constipation. In other cases, it can cause secretion of excess fluid, leading to diarrhea.
- Incontinence: The anus has sphincters (or muscles) that control the opening of the anal canal. When anal cancer grows into these muscles and damages them, a person might no longer retain control over their bowel movements. This is called incontinence.
- Mass in the anus: A tumor growing in the anus may be felt upon touching the area. Although there are other causes of anal masses (e.g. hemorrhoids), an anal mass combined with red flag symptoms like weight loss points towards anal cancer.
Anal cancer vs. colon cancer: how is the diagnosis made?
A biopsy is the only way to definitely diagnose both anal and colon cancers. This is when a doctor cuts out a part of the cancer and examines it under the microscope. But the way this tissue is taken differs for anal and colon cancer. Let’s take a deeper look:
- Anoscopy: An anoscope is a 3-4 inch tube with a camera at one end. It is used by doctors to examine the anus. It allows doctors to visualize the inside of the anus and look for any abnormal growths. If found, they can cut out a piece and send it for examination under a microscope.
- Colonoscopy: Similar to an anoscopy, a colonoscopy makes use of a long tube with a camera at the end. This is used to look inside the colon and take biopsies of any abnormal growths that are found.
- Tumor markers: Some cancers can be detected by the presence of certain molecules they release into the blood. Colon cancer can also be detected by the presence of the carcinoembryonic antigen (CEA). But there is no tumor marker specific to anal cancer.
- Computerized tomography (CT): A CT scan uses X-rays to scan the body. It can be used to scan the whole body and is therefore useful in detecting the spread of cancer, regardless of it being anal or colon cancer.
- Positron emission tomography (PET): A PET scan is used to detect cancer spread by scanning the whole body. It is particularly useful in imaging soft tissues and identifying metastasis.
Anal cancer vs. colon cancer: what is the treatment?
All solid cancers have three main treatment methods. These are anti-cancer drugs, radiation beams, and surgery. Let’s look at and compare these for anal and colon cancer.
There are several types of anti-cancer drug therapy such as chemotherapy, targeted therapy, and immunotherapy. When starting treatment with anti-cancer drugs, your doctor will likely look at established guidelines that are specific to every cancer.
Anti-cancer drugs commonly used for colon cancer include 5-fluorouracil, capecitabine, irinotecan, oxaliplatin, trifluridine, and tipiracil.
For anal cancer, a doctor might use a combination of 5-fluorouracil and mitomycin. If the anal cancer is advanced, they might add oxaliplatin, docetaxel, and cisplatin.
Radiation therapy uses strong radiation beams to kill cancer cells. It is not used commonly as a primary treatment method for colon cancer. However, it might be used along with chemotherapy (or before chemotherapy), during surgery, or after surgery to increase the effect of the primary treatment.
This is unlike anal cancer, where radiation therapy is more commonly used as the primary treatment. It can also be used in addition to other treatment methods, just like in colon cancer.
For colon cancer, surgery is very commonly used when the tumor is in its early stages. A surgical procedure called a polypectomy is frequently performed to remove cancerous polyps before they invade the gut. When the cancer is advanced, a surgeon might perform a partial or full colectomy, where the cancerous part of the colon is removed.
For anal cancer, surgery is not a primary form of treatment. It is often avoided so that the muscles in the anus can be preserved and is only performed when the cancer comes back after treatment.
Anal cancer vs. colon cancer: how do patients fare?
Generally speaking, how well patients do depends on the stage of cancer. An advanced stage means that the cancer has spread and the patients are less likely to survive, and vice versa.
Here are the statistics for colon cancer:
- Localized: For colon cancer that is confined to the colon, the 5-year survival rate is 91%.
- Regional: For colon cancer that is outside the colon but limited to nearby organs, the 5-year survival rate is 72%.
- Distant: For colon cancer that has spread to distant organs, the 5-year survival rate is 13%.
Here is how anal cancer patients fare:
- Localized: For anal cancer that is confined to the anus, the 5-year survival rate is 83%.
- Regional: For anal cancer that is outside the anus but confined to nearby tissues, the 5-year survival rate is 67%.
- Distant: For anal cancer that has spread to distant organs, the 5-year survival rate is 36%.
When should you suspect colon cancer?
Colon cancer should be suspected when you experience classic symptoms such as blood in the stool along with sudden weight loss. It should also be suspected in patients with non-specific signs and symptoms — such as diarrhea, constipation, and fatigue — but with a strong family history of colon cancer.
What is the biggest symptom of colon cancer?
The biggest symptom of colon cancer is the presence of blood in the stool. Although there are several causes of it, blood in the stool should always prompt a visit to the doctor.
How do you know if you have hemorrhoids or colon cancer?
The definitive way to differentiate between hemorrhoids and colon cancer is through a biopsy. However, your doctor might be able to differentiate between the two based on your symptoms and by examining the anus.
Is anal cancer curable?
Yes, anal cancer is curable. However, the cure rates depend on the severity of the disease.
Can you die from anal cancer?
Yes, you can die from anal cancer. This usually occurs when it has spread to other organs of the body, such as the liver, lungs, and bones.